STUDENT SPACE · TOPIC 3

Aqueous solutions

Predict products when water also supplies ions.

The essentials

In aqueous NaCl, consider Na⁺, Cl⁻, H⁺ and OH⁻.
For these aqueous examples, a metal more reactive than hydrogen stays as ions; hydrogen forms.
With inert electrodes, concentrated chloride or bromide solutions give the halogen.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

Why does aqueous NaCl give hydrogen instead of sodium at the cathode?

Need a hint for Question 1?

List all ions before choosing products. Check whether the question says molten, dilute or concentrated.

Check Question 1

Sodium is more reactive than hydrogen; hydrogen is discharged and Na⁺ remains in solution.

Predict both products from concentrated aqueous KBr using inert electrodes.

Need a hint for Question 2?

Include the ions supplied by water as well as the salt.

Check Question 2

Cathode: hydrogen. Anode: bromine.

Predict both products from dilute sulfuric acid and give the expected gas volume ratio.

Need a hint for Question 3?

Use the overall decomposition of water to determine the gas ratio.

Check Question 3

Hydrogen at cathode, oxygen at anode; H₂:O₂ = 2:1 at the same conditions.

Use Lesson 3 in your worksheet for written practice. Your teacher will discuss those answers in class.